JP2024520499A - Method and system for preventing tampering with breath sample measurements - Patents.com - Google Patents

Abstract

The present invention relates to a breath analysis system and method. In particular, the present invention relates to a breath analysis system and method for determining the validity of the measurement of the concentration of an intoxicating substance in a user's breath, thereby reducing the risk of falsifying the results without increasing the analysis time or inconvenience to the user. A gaze detector is provided, the output signal of which is compared to a tracer substance signal to determine whether the signals have respective expected behaviors and relationships.Selected Figure: Figure 2a

Description

The present invention relates to a breath analysis device and method. More specifically, the present invention relates to a breath analysis device and method that reduces the possibility of falsifying the results without increasing the analysis time or causing inconvenience to the user.

Breath analysis devices are becoming increasingly common, especially in vehicles, as a means to detect and prevent driving under the influence of intoxicating substances, especially ethyl alcohol (ethanol). Breath analysis devices can be stand-alone units that give a measurement of the content of substances in the driver's breath, or even handheld units. Alternatively, breath analysis devices can be part of a system that also includes equipment for identifying the driver and/or locking the vehicle. Such breath analysis devices are typically permanently mounted in the vehicle and can be, for example, an integrated part of the dashboard. Breath analysis devices can also be stationary systems used to restrict access to work areas, vehicle fleet depots, etc.

Providing a breath analyzer that has suitable sensitivity, is reliable and provides a sufficiently fast analysis is not an easy task. This is particularly difficult when the breath analyzer should be able to detect multiple substances and should not be hindered by variability in moisture, _CO2 content, etc. Breath analyzers that meet these requirements are described, for example, in US7919754 and US9746454, which are incorporated herein by reference.

The breath analysis device may be part of a system that also includes a device for identifying the driver and/or locking the vehicle, a so-called "alcohol interlock device". Such a breath analysis device is typically permanently installed in the vehicle and may be, for example, an integral part of the dashboard and may further be connected to the vehicle's control system. Alcohol interlock devices are widely used in offender programs as a mandatory adjunct for the rehabilitation of car owners who have been convicted of drunk driving. In addition, similar systems and devices are used in commercial vehicles such as buses, taxis, and trains. However, it is believed that these systems will soon become commonplace in private vehicles as well, and possibly mandatory in at least some countries and regions.

The most common approach for both conventional vehicle-mounted breath testing devices and fixed testing laboratories is to use a mouthpiece that allows the user to clear their airway after taking a deep breath. This approach is called active detection. To ensure an accurate result, the user must provide a forced exhalation with nearly full lung capacity. This requires significant time and effort, especially for people with limited lung capacity. In addition, the mouthpiece, or parts of the mouthpiece, are often disposable plastic items for hygienic reasons. This results in cumbersome handling and a huge amount of disposable plastic items being used, which are questionable from an environmental point of view.

Non-contact detection is an alternative approach where no mouthpiece is utilized, the breath testing device typically receives a mixture of exhaled breath and ambient air, and the detection of an intoxicating substance is determined from a breath sample taken during exhalation in normal breathing. This detection can be completely passive, e.g., no user action is required while the user is performing routine normal startup of the vehicle. Alternatively, the user can be instructed to perform a specific action intended to facilitate the detection process, e.g., the user can be instructed to breathe towards an air intake or the like. One problem with non-contact detection is the low concentration of the substance to be detected and analyzed, even when the user is instructed to breathe in a specific direction or the like. An established method is to utilize a tracer gas, typically carbon dioxide or water vapor, which is always present in the exhaled breath in very predictable amounts, both to trigger the analysis of the target substance and to facilitate the determination of the concentration value of the target substance. However, it has proven difficult to make non-contact detection work in a satisfactory manner in real-life scenarios. Accurately analyzing the concentration of an intoxicating substance can take a very long time. This required time may be perceived as unacceptably long, for example, when starting a vehicle or when an employer attempts to enter a gated work site.

One further challenge with using non-contact breath analyzer systems is that such systems may be particularly susceptible to tampering. Tampering may include, for example, cooling the breath sample with a chilled tube or filtering the breath sample with charcoal. Tampering is a recognized problem and has been addressed in a variety of ways. However, known approaches typically add significant complexity to the breath analyzer system, making it more cumbersome to use, or increasing the time required to provide a result to a user.

EP 3106872 discloses a system and method in which a breath analyzer system is provided with a camera and the images produced are analysed with advanced image analysis methods to detect and warn of tampering attempts.

The object of the present invention is to provide a breath analysis system and method of operation that overcomes the shortcomings of prior art non-contact detection systems.

This is achieved by a method as defined in claim 1 and a breath analysis device as defined in claim 10.

According to one aspect of the present invention, there is provided a method for determining the validity of a measurement of a concentration of an intoxicating substance in a user's breath using a breath analysis device, the breath analysis device comprising:
a measurement cell configured to sample a sensor signal representative of a concentration of the intoxicating substance and a sensor signal representative of a concentration of the tracer substance;
a line of sight detector having a predetermined field of view and configured to measure coverage of the field of view by objects and to output a signal representative of the coverage.
The above method is
- monitoring an output signal of the gaze detector and, if the output signal deviates from a set background value, recording the gaze detector output signal as a function of time, the output signal change being a recorded gaze signal signature;
monitoring the tracer substance sensor signal and, if a peak in the tracer substance is detected, the peak indicating a possible exhalation phase of the user's breathing cycle, deriving a value of the exhaled breath concentration of the intoxicant based on the intoxicant sensor signal and the tracer substance sensor signal;
- comparing a recorded gaze signal signature originating from the gaze detector with at least one stored reference signal signature;
comparing the relationship between the line of sight detector output signal and the tracer substance signal with stored signal relationship criteria;
- If the recorded gaze signal signature matches the stored reference signal signature and if the recorded gaze output signal and tracer substance signals satisfy the stored signal relationship criteria, the measurement of the breath concentration value is confirmed as valid.

According to one embodiment of the present invention, in the monitoring step, a background value of the gaze detector output signal is derived and the step of comparing the recorded gaze signal signature to a stored reference signal signature includes comparing at least one of the following parameters or a selection from said parameters: signal slope after initial rise, duration of the time segment during which the signal is raised, signal value associated with the upper limit value, duration of the signal above a predefined level associated with the upper limit level, signal slope after peak or plateau.

According to one embodiment of the present invention, the stored signal relationship criterion includes a time relationship between the gaze detector output signal and the tracer substance signal. The time relationship criterion may be conditioned on an increase in the recorded gaze detector output signal, indicative of an object approaching the breath analysis device, occurring before the onset of a peak in the tracer substance signal. The time relationship criterion may further be conditioned on a peak in the recorded gaze detector output signal coinciding with a peak in the tracer substance signal within a predetermined time interval. Furthermore, the step of comparing the relationship between the gaze detector output signal and the tracer substance signal with the stored signal relationship criterion may include modifying the time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined factor related to an expected time delay related to the time required for the breath sample to reach the breath analysis device. Alternatively, the time relationship between the gaze detector output signal and the tracer substance signal may include an expected time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined factor related to an expected time delay related to the time required for the breath sample to reach the breath analysis device.

According to one embodiment of the invention, the gaze detector is configured to measure thermal radiation. The breath analysis device may further comprise means for measuring ambient temperature, and the output signal from the gaze detector is compensated for the ambient temperature.

According to one aspect of the present invention, there is provided a breath analysis device comprising:
a measuring cell adapted to sample a sensor signal representative of the concentration of the intoxicating substance and a sensor signal representative of the concentration of the tracer substance;
a line of sight detector having a predetermined field of view and adapted to measure coverage of the field of view by objects and to output a signal representative of the coverage,
a control and signal processing unit connected to the measuring cell and to the line of sight detector, the breath analysis device comprising:
- monitoring an output signal of the gaze detector and, if the output signal deviates from a set background value, recording the gaze detector output signal as a function of time, the output signal change being a recorded gaze signal signature;
monitoring the tracer substance sensor signal and, if a peak in the tracer substance is detected, the peak indicating a possible exhalation phase of the user's breathing cycle, deriving an exhaled breath concentration value of the intoxicant based on the intoxicant sensor signal and the tracer substance sensor signal;
- comparing a recorded gaze signal signature derived from said gaze detector with at least one stored reference signal signature;
comparing the relationship between the line of sight detector output signal and the tracer substance signal with stored signal relationship criteria;
- If the recorded gaze signal signature matches the stored reference signal signature and if the recorded gaze output signal and tracer substance signals satisfy the stored signal relationship criteria, the measurement of the breath concentration value is confirmed as valid.

According to one embodiment of the invention, the line of sight detector is configured to detect electromagnetic radiation and includes an aperture that determines an effective field of view of the line of sight detector. The line of sight detector may include a sensor that utilizes infrared detection and is configured to measure thermal radiation.

According to one embodiment of the present invention, the line of sight detector (108) sensor is an active sensor configured to utilize near-infrared reflectance measurements.

According to one embodiment of the present invention, the gaze detector is configured to have a field of view corresponding to a predefined area at a predefined distance from the breath analysis device, the predefined area being an area of a typical human face of a person using the breath analysis device at the predefined distance, the predefined distance being associated with proper use of the breath analysis device and being between 100-300 mm.

According to one embodiment of the present invention, the breath analysis device further comprises means for measuring the ambient temperature, and the signal from the gaze detector is compensated for the ambient temperature.

According to one embodiment of the invention, the gaze detector comprises a plurality of sensors configured to provide a corresponding plurality of output signals providing a spatial resolution of the field of view that may form a low resolution image of objects within the field of view. The gaze detector may comprise an 8x8 matrix of IR photodetectors.

According to one embodiment of the present invention, the breath analysis device is further configured to derive a background value of the gaze detector output signal during the monitoring step and to compare, during the step of comparing the recorded gaze signal signature with the stored reference signal signature, one of the following parameters or a selection from said parameters: signal slope after initial rise, duration of the time segment during which the signal is raised, signal value associated with the upper limit value, duration of the signal above a predefined level associated with the upper limit level, signal slope after peak or plateau.

According to one embodiment of the present invention, the breath analysis device is further configured to store a signal relationship criterion including a time relationship between the gaze detector output signal and the tracer substance signal. The time relationship criterion may be conditioned on an increase in the recorded gaze detector output signal, indicative of an object approaching the breath analysis device, occurring before the onset of a peak in the tracer substance signal. The time relationship criterion may further be conditioned on a peak in the recorded gaze detector output signal coinciding with a peak in the tracer substance signal within a predetermined time interval. Furthermore, the step of comparing the relationship between the gaze detector output signal and the tracer substance signal with the stored signal relationship criterion may include modifying the time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined coefficient related to an expected time delay related to the time required for the breath sample to reach the breath analysis device. Alternatively, the time relationship between the gaze detector output signal and the tracer substance signal may include an expected time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined coefficient related to an expected time delay related to the time required for the breath sample to reach the breath analysis device.

The present invention provides a breath analysis method and a breath analysis device that can verify the measurement of the concentration of intoxicating substances in a user's breath.

One advantage offered by the present invention is that validation can be performed in a stand-alone unit without relying on external databases or complex image analysis systems.

A further advantage is that validation is fast and reliable, which is very important for the acceptance of implementing breath analysis systems and routines, for example in the workplace.

A further advantage of the breath analysis method and breath analysis device according to the present invention is that the method and device can be implemented in a variety of ways, including but not limited to handheld devices, fixed devices, for example at the entrance to a work area, and vehicle-mounted devices. The breath analysis device can utilize existing functions and facilities provided, for example, in an automobile infotainment system, which is easily integrated into the dashboard of the vehicle. The breath analysis device can also be communicatively connected to a vehicle lock system, a so-called alcohol interlock device.

In the following, the invention will be described in more detail, by way of example only, with respect to non-limiting embodiments thereof, with reference to the accompanying drawings, in which:

1a and 1b are schematic diagrams of a breath analysis device according to the present invention, with FIG. 1a showing the breath analysis device and FIG. 1b showing the basic concepts of line of sight and field of view. 1 is a schematic graph showing the sensor signal of a breath analysis device according to the invention, showing a typical sensor signal of a breath analysis device including a line of sight detector (upper graph) and a tracer, and a graph of a substance signal (lower graph). 2 is a schematic graph showing the sensor signal of a breath analysis device according to the present invention, and a graph and schematic diagram showing the relationship between the signal variability and the field of view of the gaze detector; FIG. 2 is a schematic graph showing the sensor signal of a breath analysis device according to the present invention, illustrating a typical signal signature and quantification of an eye gaze detector; 2 is a flow chart of a method according to the present invention; 4a, 4b and 4c are schematic diagrams of different embodiments of gaze detector arrangements according to the present invention. 1 is a graph of the spectral characteristics of one embodiment of a line of sight detector based on infrared temperature measurement; FIG. 2 illustrates an embodiment of a line of sight detector based on reflected near infrared radiation (NIR) including a graph of its field of view. FIG. 2 illustrates the field of view provided by one embodiment of a line of sight detector that uses light emitting diodes and photodiodes to monitor light reflectance within a predefined field of view. Figures 8a, 8b and 8c show schematic diagrams of different application examples of a breath analysis device according to the invention, including Figure 8a as a handheld device, Figure 8b as a wall mounted device and Figure 8c as an automobile integrated unit.

Words such as "top", "bottom", "upper", "lower", "bottom", "above" and the like are used merely to refer to the shape of the embodiments of the invention as shown in the drawings and/or during normal operation of the device, and are not intended to limit the invention in any way.

Definition:
The tracer is a physiological substance inherently associated with exhaled air, such as carbon dioxide or water vapor.

Baseline means the signal level corresponding to the concentration of the intoxicant or tracer against which other instantaneous signal values are referenced. Offset error is the deviation from the baseline.

The concentration peak is defined by the maximum of the measured concentration versus time, with an increase in concentration before the peak maximum and then a decrease thereafter.

The breath analysis device and method according to the present invention are described primarily as a non-contact detection system mounted on a vehicle, which represents an important embodiment of the present invention. The breath analysis device may be fully integrated in the vehicle, for example utilizing the existing vehicle infotainment system for communication with the user and/or the HVAC system, for example, to detect the airflow to the breath analysis device. An integrated system breath analysis device is described in SE1950840-7, which is hereby incorporated by reference. The vehicle breath analysis device according to the present invention may also be retrofitted in a vehicle, in which case the breath analysis device may typically be more independent from other parts of the vehicle instrumentation. As will be recognized by those skilled in the art, the present teachings are equally suitable for stand-alone systems, such as systems at the entrances to work areas, fleet depots, etc. The breath analysis device and method according to the present invention may also be a handheld system used in a vehicle or elsewhere.

The breath analysis devices and methods according to the present invention can be readily combined with recently developed systems and methods for improving the speed and performance of breath analysis devices, for example as described in SE1950840-7 and SE2050105-2, which are hereby incorporated by reference.

Fig. 1a is a schematic diagram of a breath analysis device 100 according to the invention. The breath analysis device 100 comprises a housing 101, a metering cell 102, a gaze detector 108, one or more audiovisual communication units 113, and a control and signal processing unit 114. The breath analysis device 100 is adapted to analyze the breath of a user within a predefined maximum distance. By deriving the concentrations of both the intoxicant and the tracer gas at this distance, the breath concentration of the intoxicant can be derived. The tracer gas has a known breath concentration, and by measuring its concentration at the position of the metering cell 102, the amount of dilution of the breath can be derived. Typically, carbon dioxide (CO ₂ ) or water vapor (H ₂ O) are used as tracer gases, which show nominal concentrations of 4.2 and 5.6 percent by volume in human breath, respectively.

The metering cell 102 is provided with an inlet 103 and an outlet 104 in the housing 101, and a means for forcing air to flow from the inlet 103 to the outlet 104, such as a fan 105. During operation, the metering cell 102 is continuously exposed to air drawn from the location of the breath sampling inlet 103. The inlet 103 is located on a surface of the housing 101 that faces the user during operation of the breath analysis device 100.

In embodiments in which the breath analysis device 100 is provided within a vehicle, the breath analysis device 100 may be fully integrated, for example into the dashboard, in which case the housing 101 is not a separate component. Also, in the case of a fully integrated device, the breath analysis device 100 may not have a dedicated audiovisual communication unit 113 and a dedicated control and signal processing unit 114, but rather utilize such functionality provided within the vehicle. These units should therefore be considered as functional units in an integrated embodiment.

The measuring cell 102 preferably operates according to the principle of infrared (IR) spectroscopy. The IR emitter 106 emits a beam of IR radiation that is absorbed by the IR detector 107 after reflection from the inner wall of the measuring cell 102. The surface of the inner wall is preferably coated with a highly reflective material, for example aluminum. The number of reflections and the collimation of the IR beam can be adapted to the expected range of IR absorption coefficients and concentrations of the tracer and intoxicating substances. The emitter 106 is typically a black body film with a small mass and is therefore adapted to emit pulsating radiation in a wide wavelength range from 3 to 10 μm with a repetition frequency of 5 Hz or more. The IR detector 107 includes a narrow band filter tuned to the absorption peak of one or several intoxicating substances, such as ethyl alcohol, with an absorption peak at a wavelength of 9.5 μm, and one or several tracer gases, such as carbon dioxide and water vapor, exhibiting absorption peaks at 4.3 and 6.0 μm, respectively. The presence of an intoxicant or a tracer gas results in a reduction in IR intensity, which is converted into an electrical signal by a multi-channel IR detector 107 having an optical filter adapted to a specific absorption peak and operating in synchronization with the repetition rate of the IR emitter 106. As will be appreciated by those skilled in the art, other types of measurement cells operating according to different principles may also be utilized. The choice of measurement cell or measurement principle may depend, for example, on the specific intoxicant to be analyzed or on construction constraints such as power consumption or cost. The present invention is not limited to a specific measurement cell or measurement principle for breath concentration measurement of a specific breath concentration of an intoxicant.

The gaze detector 108 is arranged to provide information when an object is presented and accurately positioned with respect to the inlet 103 so that the breath sample can be accurately analyzed. This is referred to as the gaze detector 108 being arranged to provide an object presence signal. The gaze detector 108 is further arranged to provide information, referred to as a signal signature, regarding the nature of the object, i.e. whether the object is a living human or not. A number of different measurement techniques implemented by the various gaze detectors are further described below.

As shown diagrammatically in FIG. 1b, the gaze detector 108 has a defined effective field of view, denoted Ω. This field of view is typically provided as a solid angle quantified in steradians. Alternatively, this field of view can be given as an angle α in the horizontal or vertical direction, or as a combination of angles α and β in the horizontal and vertical directions, respectively. The gaze detector typically has an inherent field of view from the basic design. This inherent field of view can be modified by providing further means such as one or more lenses and/or an aperture in front of the gaze detector 108 that provides an effective field of view Ω, depending on how the gaze detector 108 is mounted in the housing 101. Those skilled in the art who have gaze detectors with inherent fields of view know how to provide means to change the angle of view for a desired effective field of view. The field of view is typically fixed, but means for adjusting the field of view can be envisioned. The gaze detector 108 when mounted in the housing 101 further has a field of view direction, denoted by arrow A, that defines a possible centerline of the field of view in FIG. 1b. The line of sight direction typically depends mainly on how the gaze detector 108 is mounted in the housing 101 and/or how the entire breath analysis device 100 is mounted, for example, on a dashboard. The gaze detector 108 and the means for controlling the field of sight, if they are required, are typically arranged in the housing such that the effective field of sight and the field of sight direction coincide with the position and coverage of the user's face during normal operation of the breath analysis device 100. Typically, the user is instructed to exhale towards the inlet 103 within a predefined maximum distance between the subject's face and the inlet 103, typically 100-300 mm. A typical face with a height/width of 200 mm and 150 mm respectively may give angles α and β in the range of 20-100°. As mentioned above, the field of sight and also the field of sight direction may be adjustable, for example, by adjusting the shape of the detector or the optical arrangement. In one embodiment, the field of sight and/or the field of sight direction are parameters that are adjustable by the control and signal processing unit 114.

The gaze detector 108 is typically positioned laterally to the breath sampling inlet 3 of the measurement cell 102 on the outer surface 101a of the breath analysis device 101. The field of view α of the gaze detector 108 is adapted to be encompassed by the subject's face at a predefined maximum distance. The gaze detector 108 comprises a sensor 111, e.g. typically a multi-layer microstructure 111, and provides an electrical signal corresponding to the average temperature, reflectance, or other specific property of objects within its field of view. The active area of the microstructure 111 is typically 0.3×0.3 mm.

The field of view is adapted to a predefined distance by an optical device 110, typically a refractive lens.

According to one embodiment, the breath analysis device 100 is provided with an auxiliary sensor 112 adapted to monitor the immediate environment, for example the ambient temperature. This may be beneficial, for example, if the gaze detector 108 is an IR sensor and p may have some cross-sensitivity to the ambient temperature. By measuring both radiative and conductive heat effects and combining the signals, the influence from the ambient temperature may be minimized. The auxiliary sensor 112 may be arranged to measure other ambient variables as well, including humidity, air pressure, and illuminance.

The breath analysis device 100 may further include or be connected to a power source (not shown) and data communication means (not shown) for bidirectional transfer of information between the breath analysis device 101 and other electronic devices, such as means for controlling the vehicle's maneuverability.

The functionality and method of the breath analysis device 100 according to the invention enabling the measurement of the concentration of an intoxicating substance in the breath of a user will first be described in a general case with reference to the schematic graphs of Figs. 2a-c and the flow chart of Fig. 3, followed by a description of different embodiments utilizing different detector technologies relating to the gaze detector 108. Fig. 2a shows the output signal from the gaze detector 108 and the output from the measurement cell 102, where the upper curve indicated with T relates to the tracer signal and the lower curve S relates to the substance signal.

The breath analysis device 100 described with reference to Figs. 1a-1b is configured to carry out the steps of the method. In particular, the measurement cell 102 of the breath analysis device 100 is configured to sample a sensor signal representative of the concentration of an intoxicating substance and a sensor signal representative of the concentration of a tracer substance, preferably but not exclusively by the IR-based technology mentioned above. The functionality is controlled by the control and signal processing unit 114, and the sensor/detector signals are processed by the control and signal processing unit 114. The gaze detector 108 is configured with a predetermined field of view Ω and is configured to measure the coverage of the field of view by an object and to output a signal representative of the coverage.

The method according to the invention, which is carried out using the breath analysis device 100 and controlled by the control and signal processing unit 114, comprises the steps of:
305:- monitoring the output signal of the line of sight detector 108;
310: - if the output signal deviates from the set background value,
315: - recording an eye gaze detector output signal as a function of time, the output signal change being a recorded eye gaze signal signature;
320: - monitor tracer material sensor signals;
325: - if a peak in the tracer material is detected, the peak indicates a possible expiratory phase of the user's breathing cycle;
330: - Deriving a breath concentration value of the intoxicant based on the intoxicant sensor signal and the tracer substance sensor signal.
The effectiveness of measuring breath concentration values is
335-340: - comparing the recorded gaze signal signature from the gaze detector 108 with at least one stored reference signal signature to determine whether the recorded gaze signal signature matches the stored reference signal signature, thereby indicating that a human is approaching the breath analysis device 100;
345-350: - Comparing the relationship between the line of sight detector output signal and the tracer substance signal to stored signal relationship criteria to determine if the recorded line of sight output signal has an expected relationship to the tracer substance signal.
355: - The derived breath concentration value of the intoxicant is determined to be a valid measurement in the sense that it has not been tampered with if both the recorded gaze signal signature matches the stored reference signal signature and the gaze detector output signal and the tracer substance signal satisfy the stored signal relationship criteria.

Step 305 of monitoring the output signal of the gaze detector 108 and steps 310-315 of recording the gaze signal signature may typically include setting a background or baseline value. This may be an output signal value sampled and averaged over one or several seconds. A deviation from the background level indicative of an object in the field of view of the gaze detector 108 is detected to trigger the recording of the gaze signal signature. The manner in which this detection is performed is further described below. The level 20 shown in FIG. 2a is a representation of a typical background signal, and the upper level 21 is a representation of the signal caused by an object in the field of view. Depending on the time that the object or person remains in the field of view of the gaze detector 108, the upper level 21 may have the form of a plateau, a broad peak, or a narrow peak. A narrow peak corresponds to the person leaning towards the breath analysis device 100 and moving back slightly or continuously.

According to one embodiment, the gaze signal signature comprises, for example, a time change in the signal above the upper level 21 shown in FIG. 2b, which may be considered as an object moving or detecting an action of the object, for example, exhalation. For example, a thermal change caused by exhalation may be detected by the gaze detector 108 in the form of an IR sensor.

According to an embodiment of the present invention in steps 345-350 of comparing the relationship between the output signal of the gaze detector 108 and the tracer substance signal, the stored signal relationship criterion includes an expected time relationship between the gaze detector output signal and the tracer substance signal. This time relationship criterion may be that the rise in the recorded gaze detector output signal, indicating that an object is approaching the breath analysis device 100, occurs before the start of the peak 44 in the tracer substance signal. The time relationship criterion may also be that the peak in the recorded gaze detector output signal matches a peak in the tracer substance signal within a predetermined time interval. This comparison may include modifying the time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined coefficient related to the expected time delay related to the time required for the breath sample to reach the breath analysis device. Alternatively, this time delay between the peak in the gaze detector output signal and the peak in the tracer substance may be a relationship criterion in itself in that a predictable time delay may be associated with the correct and normal behavior of a user using the breath analysis device 100. On the other hand, if a user were to tamper with the measurement by, for example, using _CO2 supplied from a tube closer to the inlet 103, this would result in a different time delay than expected.

According to an embodiment of the present invention, steps 335-340 of comparing the recorded signature signal with the stored reference signal signature include at least comparing one or a selection of the following parameters: signal slope after the initial rise, duration of the time segment during which the signal rises, signal value associated with the upper limit value 21 (plateau value), duration of the signal above a predefined level associated with the upper limit level 21, signal slope after the peak or plateau. Suitable parameters and how they may be utilized are illustrated diagrammatically in Fig. 2b-c. Fig. 2b) provides an illustration of the line-of-sight LoS signal, the synchronized tracer T signal, and the presence of a human face appearing in the field of view of the line-of-sight detector. Initially, the field of view represents a background that may be unstructured as shown, or structured but fixed surface. When a human face appears in the field of view, the line-of-sight signal changes from a steady-state background level and reaches an upper limit level, typically in the form of a plateau or a broad peak, when most of the field of view is covered. Some signal changes can be observed at this upper level, corresponding to small movements of the human face, as well as changes in the shape of the mouth opening and exhalation, for example. The tracer signal T typically exhibits a distinct peak that coincides with the human exhaling. As the human face exits the field of view, the gaze signal plateaus and returns to the background level.

Fig. 2c) illustrates in somewhat more detail the gaze signal from the gaze detector as a function of time. The signal can be divided into time segments, each of which is characterized by its signal slope characteristic. The transitions between segments are defined as the intersection of a linear extension between the segment and coordinates L _i ; t _i , i=1,2,...8 in this example. The coordinates L _i ; t _i in this example define the signal signature. In particular, the nearly flat time segment 0-t ₁ represents the background signal, t ₁ -t ₂ represent a sharp rise that coincides with the entry of an object, typically the human face under inspection, into the field of view, t ₅ -t ₆ represent a plateau where the object fills the field of view, and t ₆ -t ₇ represent the start of the decline as the object moves out of the field of view. The additional time segments t ₂ -t ₃ , t ₃ -t ₄ , t ₄ -t ₅ , t ₇ -t ₈ are intermediate states that may or may not be significant for interpretation of the signal signature.

Identification of the coordinates of L _i ;t _i is performed by a simple algorithm that uses the derivative of successive time samples to provide the current slope value and compare it with the previous time sample.

In the example described above and shown in Fig. 2c), the stored reference signal signature is a parameter set of L _i ;t _i coordinates, i = l, 2, ... N, with characteristics of (i) background stationary phase, (ii) rising phase, (iii) plateau, (iv) start of falling phase. The set of reference L _i ;t _i coordinates typically includes a tolerance for normal variability based on empirical data obtained from actual implementations of gaze detectors.

When comparing one gaze signal with another gaze signal with a slightly different field of view, the two signals clearly have almost equal appearance, except for a slight time delay caused by the translational movement of the object entering or leaving the field of view. Thus, the coordinates L _i ; t _i are slightly different in time between the two signals in such cases. In contrast, the time change of the shape of the object, such as opening the mouth, does not provide a similar time difference of the L _i ; t _i coordinates. When several objects move independently of each other, the time difference between L _i ; t _i does not show a very orderly time change, indicating a manipulation attempt.

According to one embodiment, the gaze signal signature relates to the gaze detector 108 with additional spatial resolution, whereby signal changes over time may also be attributed to specific regions. For example, a simple array of IR sensors resolves time-dependent thermal changes localized to a portion of an object into an "image" that may occur if the object is a human face exhaling warm breath. By using a composite signal from two or several regions, it is possible to distinguish between translational motion of an object and changes in the object's shape. Translational motion manifests itself in the time difference between signal signatures representing nearby but different fields of view. On the other hand, signal signatures resulting from shape changes occur simultaneously in two nearby fields of view.

According to one embodiment in which the gaze detector 108 is a passive IR sensor operating in the wavelength range 5-8 μm and whose output signal corresponds to the average temperature of objects within its field of view, the following signal characteristics are valid: The difference between the plateau level 21 and the background level 20 corresponds to the difference between the skin temperature of a person's face and the average temperature of the background when the person's face is not within the field of view of the gaze detector 108.

According to one embodiment in which the line of sight detector 108 comprises a light emitting diode illuminating a predefined field of view and a photodiode configured to detect reflected light from essentially the same field of view, the background level 20 and the upper limit level 21 each correspond to the average reflectance of objects within the field of view. Disturbances from external light sources can be minimized by synchronous operation between the light emitting diode and the photodiode, and by selecting an operating wavelength range of 0.8 to 1.0 μm, slightly above the visible range.

A common characteristic of each embodiment of the line of sight detector 108 is that electromagnetic radiation is used in either a passive or active mode of operation. The line of sight detector 108 of the embodiment includes an aperture that directly or indirectly determines the actual field of view. To avoid undesirable effects of wave diffraction, this aperture is preferably much larger than the operating wavelength range. Figures 4a-c show the line of sight detector 108 in three alternative embodiments including an optical device 110 that defines the field of view 109 and a sensor 111 in the form of a multilayer microstructure 111.

It should be understood that several passive and active sensor principles may be used for the sensor 111. Infrared thermometry is an example of a passive sensor, where the narrow skin temperature range of the human face provides useful contrast against the background. The use of near-infrared (NIR) reflectance measurements is an example of an active sensor, where the field of view is defined by a well-defined diverging beam of NIR radiation. The presence of a diffusely reflecting object within the field of view provides a reflectance signal that can be detected by a photodiode in close proximity to the NIR emitter.

The line-of-sight detector device 408a of FIG. 4a is based on the line-of-sight principle, including an aperture 410a having a width w that defines a field of view 405a.

A predefined distance D _a between the face of the person under test, having a width F _a , and the aperture 410 a defines the field of view 405 a by an angle q _a , where tan q _a /2=F _a /2D _a . Furthermore, the width w of the aperture 410 a, the size s of the microstructures 411 a, and the distance _da between the outer surface of the breath analysis device 100 and the surface of the microstructures 411 a are given by equation (1).

By using equation (1), w can be determined when F _a , D _a , d _a , and s are known. Using the values F _a =150 mm, D _a =100 mm, s=0.3 mm, and d _a =0.5 mm, an aperture width w=0.45 mm is appropriate. Thus, the configuration shown in FIG. 3a) is appropriate for a relatively short distance D _a . A human adult face typically has an elliptical shape with approximate widths of 150 mm and 200 mm in the horizontal and vertical directions, respectively. The shape of the aperture 410a can be selectively elliptical or oval correspondingly.

An embodiment of the gaze detector device 408b is shown diagrammatically in Fig. 3b) and comprises an optical device 410b suitable for a longer distance between the person's face and the outer surface of the housing 101 of the breath analysis device 100. The optical device 410b comprises a refractive lens 410b, preferably microstructured, provided to focus the thermal radiation from the person's face _Fb onto the sensor 411b. The distances _Db and _db are defined as shown in Fig. 3b). The focal length f of the lens can be calculated from equation (2):

The relationship between the sizes s of the microstructures 11b is given by equation (3).

Substituting the following values D _b =300 mm, d _b =0.6 mm, and s=0.3 mm results in f=0.6 mm and F _b =150 mm. Thus, the optical device 110 b provides an adequate field of view for a distance D _b =300 mm between a person's face having a width F _b =150 mm and the outer surface of the breath analysis device 101.

The material of lens 410b should preferably have a refractive index of 1.5-1.7 and low absorption in the wavelength range of 5-8 μm for passive IR temperature measurement sensors and 0.8-1.0 μm for NIR reflectance sensors. Polyethylene and polyester (Mylar™) are examples of polymers with sufficient infrared transmission properties. Suitable spherical or parabolic lens shapes can be obtained by injection molding or die casting of the polymer material.

One embodiment of the line of sight detector device 408c is shown diagrammatically in FIG. 4c and comprises an optical device 410c with multiple lenses 410d, 410e, 410f, each exhibiting different fields of view and focal lengths that allow the radiant heat detection to be split into separate regions, and multiple sensors 411c, 411d, 411e, preferably microstructured, located in one or several image planes to allow different apertures and angular fields of view. As will be appreciated by those skilled in the art, the device with three lenses and three sensors shown is a non-limiting example. More lenses/sensors may be provided, for example in a 2D-array. By adding information about the angular heat distribution, a more accurate analysis of the combined signal from the sensors 411c, 411d, 411e can be achieved.

Figure 5 shows a graph of the infrared spectral distribution of thermal radiation from a black body BB at a temperature of 35°C in the wavelength range of l = 2-10 μm according to the Planck equation for black body radiation. Human skin exhibits an emissivity coefficient of about 0.95 regardless of skin color, and therefore the calculated thermal radiation from a black body is an accurate approximation of the thermal radiation from human skin. As the temperature increases from 35°C, the graph shown for BB shifts towards shorter wavelengths and also increases in magnitude, as is evident from the Planck equation. Thus, a measurement of the radiant power in one or several wavelength intervals is an indirect measurement of the surface temperature.

Also shown in the graph of FIG. 5 is the spectral response of a photovoltaic multilayer microstructure based on the III-V semiconductor indium arsenide antimonide InAsSb, which may be advantageously used as the sensor 111. The multilayer microstructure includes at least one layer exhibiting a depletion of charge carriers, electrons, or holes. The depletion layer can be created by a pn junction between p or n dopant materials, or by a Schottky barrier. When a photon with the appropriate energy is absorbed in this layer, a charge and a voltage are generated. The detailed response characteristics of the curve labeled "InAsSb" in FIG. 5 are determined by the energy band gap of the semiconductor material, which can be modified by substitution between the elements arsenic As and antimony Sb. With such compositional variations, the dip occurring at longer wavelengths can be shifted to shorter wavelengths by as much as 1.5 μm.

By combining several microstructures with different spectral distributions compared to the curve InAsSb, the accuracy of skin temperature measurement can be significantly improved. Photovoltaic microstructures with sufficient properties are commercially available from Asahi Kasei Electronics, Tokyo, Japan, product lines AK9752, AK9754, AK9756.

The photovoltaic microstructure may include sensor elements that respond to thermal conduction in addition to photovoltaic elements that respond to thermal radiation. Beneficially, it may also include Peltier elements that allow the microstructure to be heated or cooled to pre-set and controlled temperatures.

The spectral transmission curve of the long-pass filter LP is also included in the graph of FIG. 5. The long-pass filter LP can be inserted in the optical path of the sensor 111 to minimize cross-sensitivity to interference from light sources emitting at shorter wavelengths. Long-pass or band-pass transmission characteristics can be achieved using a variety of inorganic and polymeric materials (S. Musicant Optical Materials, 1985, pp. 176-199). The spectral distributions in FIG. 5 are normalized to the maximum emission (E), response (R), and transmission (T) of the blackbody radiator, photovoltaic microstructure, and long-pass filter, respectively.

The sensor 111 in the form of a photovoltaic microstructure has a distinct advantage, for example, compared to a thermopile operating by the thermoelectric principle in providing a true DC response. Thermoelectric devices require a temperature difference between two or more locations, setting a low frequency limit for operability. Thus, limitations due to heat conduction and compact design reduce the attractiveness of thermoelectric devices compared to photovoltaic structures. An additional advantage of photovoltaic microstructures is their superior resolution resulting in a higher signal-to-noise ratio.

Figures 6 and 7 show representations of the field of view obtained with two types of devices as examples of physical implementations of the invention.

The graph in Figure 6 shows the horizontal and vertical angular distribution of the field of view obtained with a commercially available 8x8 matrix IR photodetector (Panasonic AMG88). The line of sight detector according to the present embodiment allows the field of view to be divided into a low-resolution image. The full field of view of ±30 degrees in each of the horizontal and vertical directions can be divided into 8x8=64 separate elements, and the line of sight signal can be composed of a composite of some of the signals from each of the 64 elements.

The graph in Figure 7 represents an example of the field of view provided by a line of sight detector that includes a commercially available light emitting diode and photodiode (VCNL3040, Vishay Semiconductors, Inc.) that monitors the reflectance of objects in the vicinity. As shown in the graph, the field of view is represented by an annular reflectance distribution with a 50% falloff at ±15 degrees.

Figure 8 shows a typical operation of a breath analysis device according to the present invention, which may be incorporated into a handheld device 81a as shown in Figure 8a, a freestanding wall-mounted instrument 51b as shown in Figure 8b, or a unit 51c integrated into, for example, the steering wheel (as shown) or dashboard of a vehicle as shown in Figure 8c.

As shown in FIG. 8a, in the case of a handheld device 51a, the user is instructed via the communication unit 113 to grasp the device 51a in his/her hand, bring it within a predefined distance, and then exhale towards it.

As shown in FIG. 8b, in the case of a wall-mounted freestanding device 51b, the user is instructed via the communication unit 113 to approach the device 51b until a predefined distance is reached and then exhale towards it.

As shown in FIG. 8c, in the case of unit 51c integrated into a vehicle steering wheel or the like, the person being tested is instructed via communication unit 113 to bend towards unit 51c, thereby bringing it within a predefined distance, and then to exhale towards it.

A change in the relative distance between the user and the breath analysis device 100, either as a result of the user moving closer to the device or leaning towards the device, results in an eye gaze detector signal according to the graphs of Figures 2a-2c. The details in the eye gaze detector signal signature will vary depending on the implementation intended to be considered when setting the reference signal signature that stores the reference signal utilized in the manner described with reference to Figure 3. Those skilled in the art will readily come up with suitable reference signal signatures relevant to a particular implementation based on a limited set of experiments in which a typical and preferably user tests the device.

The above-described embodiments should be understood as illustrative examples of the system and method of the present invention. Those skilled in the art will appreciate that various modifications, combinations and variations can be made to the above-described embodiments. In particular, different part solutions in different embodiments can be combined in other configurations, where technically possible.

Claims (23)

A method for determining the validity of a measurement of a concentration of an intoxicating substance in a user's breath using a breath analysis device (100), comprising:
The breath analysis device (100)
a measuring cell adapted to sample a sensor signal representative of the concentration of the intoxicating substance and a sensor signal representative of the concentration of a tracer substance;
a line of sight detector having a given field of view and adapted to measure the coverage of said field of view by an object and to output a signal representative of the coverage,
The method comprises:
(305) monitoring the output signal of the gaze detector (108) and (310) if the output signal deviates from a set background value, (315) recording the gaze detector output signal as a function of time, the output signal change being a recorded gaze signal signature;
(320) monitoring the tracer substance sensor signal, (325) determining if a peak in the tracer substance is detected, said peak indicating a possible exhalation phase of the user's breathing cycle, and (330) deriving an exhaled breath concentration value of the intoxicant based on the intoxicant sensor signal and the tracer substance sensor signal;
(335) comparing said recorded gaze signal signature originating from said gaze detector (108) with at least one stored reference signal signature;
(345) comparing the relationship between said line of sight detector output signal and said tracer substance signal with stored signal relationship criteria;
(340, 350, 355) if the recorded gaze signal signature matches the stored reference signal signature and if the recorded gaze output signal and tracer substance signals satisfy the stored signal relationship criteria, the validity of the measurement of the breath concentration value is confirmed. The method of claim 1, wherein in the monitoring step (305), a background value of the gaze detector output signal is derived, and the step (335) of comparing the recorded gaze signal signature to the stored reference signal signature includes comparing at least one of the following parameters, or a selection from the following parameters: signal slope after an initial rise, duration of a time segment during which the signal rises, a signal value associated with an upper limit value (21), duration of a signal above a predefined level associated with the upper limit level (21), signal slope after a peak or plateau. The method of any of claims 1 and 2, wherein the stored signal relationship criteria includes a time relationship between the line of sight detector output signal and the tracer substance signal. The method of claim 3, wherein the time-related criterion is that a rise in the recorded line-of-sight detector output signal, indicative of an object approaching the breath analysis device (100), occurs before the onset of the peak in the tracer substance signal. The method of claim 4, wherein the time relationship criterion is that a peak in the recorded line of sight detector output signal coincides with the peak in the tracer substance signal within a predetermined time interval. The method of claim 5, wherein the step (345) of comparing the relationship between the gaze detector output signal and the tracer substance signal with stored signal relationship criteria includes modifying the time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined factor related to an expected time delay related to the time required for a breath sample to reach the breath analysis device (100). 3. The method of claim 2, wherein the time relationship between the gaze detector output signal and the tracer substance signal comprises an expected time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined factor related to an expected time delay related to the time required for a breath sample to reach the breath analysis device (100). The method of any one of claims 1 to 7, wherein the line of sight detector (108) is configured to measure thermal radiation. The method according to any one of claims 1 to 8, wherein the breath analysis device (100) further comprises means for measuring an ambient temperature, and the output signal from the gaze detector (108) is compensated for the ambient temperature. A breath analysis device (100) configured to perform a measurement of a concentration of an intoxicating substance in a user's breath and to verify said measurement, comprising:
The breath analysis device (100)
a measuring cell (102) adapted to sample a sensor signal representative of the concentration of said intoxicating substance and a sensor signal representative of the concentration of a tracer substance;
a line of sight detector (108) having a given field of view and adapted to measure the coverage of said field of view by an object and to output a signal representative of the coverage;
a control and signal processing unit (114) connected to said measuring cell (102) and to said line of sight detector (108), said breath analysis device (100) comprising:
(305) monitoring the output signal of the gaze detector (108) and (310) if the output signal deviates from a set background value, (315) recording the gaze detector output signal as a function of time, the output signal change being a recorded gaze signal signature;
(320) monitoring the tracer substance sensor signal, (325) determining if a peak in the tracer substance is detected, said peak indicating a possible exhalation phase of the breathing cycle of the user, and (330) deriving an exhaled breath concentration value of the intoxicant based on the intoxicant sensor signal and the tracer substance sensor signal;
(335) comparing said recorded gaze signal signature originating from said gaze detector (108) with at least one stored reference signal signature;
(345) comparing the relationship between the line of sight detector output signal and the tracer substance signal with stored signal relationship criteria;
- (340, 350, 355) if the recorded gaze signal signature matches the stored reference signal signature and if the recorded gaze output signal and the tracer substance signal satisfy the stored signal relationship criteria, the validity of the measurement of the breath concentration value is confirmed, the breath analysis device (100). The breath analysis device (100) of claim 10, wherein the gaze detector (108) is configured to detect electromagnetic radiation and includes an aperture that determines an effective field of view of the gaze detector (108). The breath analysis device (100) of claim 10 or 11, wherein the line of sight detector (108) comprises a sensor (111) using infrared detection and configured to measure thermal radiation. The breath analysis device (100) of claim 12, wherein the sensor (111) of the gaze detector (108) is an active sensor configured to utilize near-infrared reflectance measurements. The breath analysis device (100) according to any of claims 10 to 13, wherein the gaze detector (108) is configured to have a field of view corresponding to a predefined area at a predefined distance from the breath analysis device, the predefined area being an area of a typical human face of a person using the breath analysis device (100) at the predefined distance, the predefined distance being associated with proper use of the breath analysis device (100) and being between 100 and 300 mm. The breath analysis device (100) according to any one of claims 10 to 14, further comprising means for measuring an ambient temperature, and the signal from the gaze detector (108) is compensated for the ambient temperature. The breath analysis device (100) of any one of claims 10 to 15, wherein the gaze detector (108) comprises a plurality of sensors (411c, 411d, 411e) configured to provide a corresponding plurality of output signals providing a spatial resolution of the field of view. The breath analysis device (100) of any one of claims 10 to 15, wherein the line of sight detector (108) comprises an 8x8 matrix of IR light detectors. In the monitoring step (305), a background value of the gaze detector output signal is derived, and the step (335) of comparing the recorded gaze signal signature with the stored reference signal signature includes comparing at least one of the following parameters or a selection from the following parameters: signal slope after an initial rise, duration of a time segment during which the signal rises, a signal value associated with an upper limit value (21), duration of a signal above a predefined level associated with the upper limit level (21), signal slope after a peak or plateau. A breath analysis device (100) according to any of claims 10 to 15. The breath analysis device (100) of any one of claims 10 to 18, wherein the stored signal relationship criteria includes a time relationship between the line of sight detector output signal and the tracer substance signal. 20. The breath analysis device (100) of claim 19, wherein the time-related criterion is that a rise in the recorded gaze detector output signal indicating an object is approaching the breath analysis device (100) occurs before the onset of the peak in the tracer substance signal. The breath analysis device (100) of claim 20, wherein the time relationship criterion is that a peak in the recorded gaze detector output signal coincides with the peak in the tracer substance signal within a predetermined time interval. 22. The breath analysis device (100) of claim 21, wherein the step (345) of comparing the relationship between the gaze detector output signal and the tracer substance signal with stored signal relationship criteria includes modifying the time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined coefficient related to an expected time delay related to the time required for a breath sample to reach the breath analysis device (100). 20. The breath analysis device (100) of claim 19, wherein the time relationship between the gaze detector output signal and the tracer substance signal includes an expected time difference between the peak in the gaze detector output signal and the peak in the tracer substance by a predetermined coefficient related to an expected time delay related to the time required for a breath sample to reach the breath analysis device (100).

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